The invention relates to the field of gas phase polymerization reactions. In particular, the invention is directed to novel solid supported gas phase anionic polymerization catalysts for the production of diene elastomers, especially styrene butadiene rubber (SBR).
Gas phase fluidized bed, stirred or paddle-type reactor processes for the production of polymers, such as poly-.alpha.-olefins and polybutadiene having highly desirable and improved properties, are well known. These gas phase processes, especially the gas fluidized bed process, provide a means for producing polymers with a drastic reduction in capital investment expense and a dramatic savings in energy usage and operating costs, as well as a greater margin of safety and fewer environmental concerns, compared to other conventional polymerization processes. The polymer products of gas phase polymerization processes are free-flowing granular powders that are readily compounded to form rubber products.
As in solution polymerization processes, a catalyst is usually required for polymerization of monomers in gas phase polymerization. However, the catalysts employed in gas phase polymerization of .alpha.-olefins such as ethylene or propylene, or conjugated dienes such as butadiene, have hitherto been limited to solid supported Ziegler-Natta type catalysts based on titanium, vanadium and the like, solid supported chromium salts, Group VIII transition metal compounds, or other solid supported or solution transition metal coordination catalysts, and the like. Catalysts that exhibit activity in solution phase anionic polymerization reactions and those which operate by ionic or free radical mechanisms are typically not suitable for gas phase polymerization processes. Thus, none of the catalysts conventionally used in gas phase polymerization is capable of anionically copolymerizing conjugated dienes to form diene rubbers, which are the key raw materials used in the production of rubber tires.
Moreover, one of the disadvantages associated with supported gas phase catalysts is that the support material such as alumina, silica, and the like, remains behind in the polymer product as inorganic residual ash thereby increasing the overall impurity level of the polymer. Depending on the amount of such impurity, some of the properties of the polymers may possibly be affected, such as film appearance rating, impact resistance, tear strength, and the like. Another disadvantage of known gas phase polymerization processes using these catalysts is that they typically require undesirably large quantities (e.g., 30% in the product) of powdering filler materials, such as carbon black, in order to reduce the "stickiness" of the resulting polymer and prevent the agglomeration of the resin particles and the formation of large polymer chunks.
Because of the advantages of gas phase polymerization compared with solution polymerization, however, it would be useful to provide a gas phase anionic polymerization process by which diene elastomers, such as styrene butadiene rubber, polybutadiene rubber, polyisoprene rubber, and the like, can be economically and efficiently produced.